tg3: Reduce 57765 core clock when link at 10Mbps

This patch reduces the core clock to 6.25MHz when operating at 10Mbps
link speed.  This is needed to prevent a bug that will ultimately cause
transmits to cease.
Signed-off-by: NMatt Carlson <mcarlson@broadcom.com>
Reviewed-by: NMichael Chan <mchan@broadcom.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/tg3.c

@@ -7654,6 +7654,11 @@ static int tg3_reset_hw(struct tg3 *tp, int reset_phy)
 		     val | TG3_PCIE_PL_LO_PHYCTL5_DIS_L2CLKREQ);
 
 		tw32(GRC_MODE, grc_mode);
+
+		val = tr32(TG3_CPMU_LSPD_10MB_CLK);
+		val &= ~CPMU_LSPD_10MB_MACCLK_MASK;
+		val |= CPMU_LSPD_10MB_MACCLK_6_25;
+		tw32(TG3_CPMU_LSPD_10MB_CLK, val);
 	}
 
 	/* This works around an issue with Athlon chipsets on